Recoverable articles have found wide use for environmental sealing because of the ease with which they can be installed, the strength of seal that can be obtained, and the wide range of size of substrates with which any one design can be used. Recovery can be initiated by various means, although heat-recovery is at present preferred since heat-recoverable products are simple to produce and do not require specialized equipment to install. The article is simply placed over the substrate to be protected and heated which causes it to recover, generally by shrinking, into close conformity with the substrate.
A heat-recoverable article (an article the dimensional configuration of which may be made substantially to change when subjected to heat treatment) usually will recover towards an original shape from which it has previously been deformed but the term "heat-recoverable", as used herein, also includes an article which, on heating, adopts a new configuration, even if it has not been previously deformed.
In their most common form, such articles comprise a heat-shrinkable sleeve made from a polymeric material exhibiting the property of elastic or plastic memory as described, for example, in U.S. Pat. Nos. 2,027,962; 3,086,242 and 3,597,372. As is made clear in, for example, U.S. Pat. No. 2,027,962 the original dimensionally heat-stable form may be a transient form in a continuous process in which, for example, an extruded tube is expanded, whilst hot, to a dimensionally heat-unstable form but, in other applications, a preformed dimensionally heat-stable article is deformed to a dimensionally heat-unstable form in a separate stage.
In the production of heat recoverable articles, the polymeric material may be cross-linked at any stage in the production of the article that will enhance the desired dimensional recoverability. One manner of producing a heat-recoverable article comprises shaping the polymeric material into the desired heat-stable form, subsequently cross-linking the polymeric material, heating the article to a temperature above the crystalline melting point or, for amorphous materials the softening point, as the case may be, of the polymer, deforming the article and cooling the article whilst in the deformed state so that the deformed state of the article is retained. In use, since the deformed state of the article is heat-unstable, application of heat will cause the article to assume its original heat-stable shape.
In other articles, as described, for example, in British Pat No. 1,440,524, equivalent to U.S. Pat. No. 4,035,534 an elastomeric member such as an outer tubular member is held in a stretched state by a second member, such as an inner tubular member, which, upon heating weakens and thus allows the elastomeric member to recover.
Heat recoverable wrap-around or tubular articles, referred to generally as sleeves although they may be more complex than simple cylinders and may have some closed ends, have been successfully involved in many fields of applications. However, problems may arise when two or more substrates such as supply lines, for example cables or pipes, have to be sealed at one position. This problem, which is known as branch-off, may occur for example at the outlet of a heat-recoverable article. Amongst areas where this problem is typically encountered there may especially be mentioned outlets of telecommunications splice cases, and feedthrough devices.
One effective solution to the problem of branch-off has been to use moulded heat-shrinkable articles provided with preformed outlets for individual supply lines. However, in general such outlets have to be made to suit a specific application, and since they are expensive their use has not been widespread.
A less expensive solution is to use mastic tape to seal the gap between the supply lines so that on recovery of the heat recoverable article a proper encapsulation is formed. However, use of such tape requires skill and the method is not applicable to large branch-offs.
The problem was overcome by the surprising discovery that an effective branch-off at the end of a heat-recoverable article can be obtained by forming the individual outlets by means of a suitably shaped clip. This technique is disclosed in UK Pat. No. 2019120, equivalent to U.S. Pat. No. 4,298,415, which claims a method of forming a branch-off seal between a heat-shrinkable sleeve and at least two substrates, which comprises the steps of:
(a) positioning a clip having at least two elongate legs on the heat-shrinkable sleeve at an open end thereof with at least two of said legs being positioned externally of the sleeve so as to form at least two terminal conduits;
(b) positioning the substrates within the conduits; and
(c) applying heat so as to effect shrinkage and to form the desired seal.
Excellent results have been achieved using this technique, high performance seals being easily produced from a small inventory. For certain branch-off configurations and where the seal is likely to be subjected to high pressure it has been found desirable to provide a sealing material such as a hot-melt adhesive in the crutch region between the diverging substrates and the surrounding recoverable sleeve. The above-mentioned patent also describes and claims use of a clip having three legs, where the outer legs perform the clipping function and an inner leg serves to deliver adhesive to the crutch region. When this adhesive is heat-activated (for example by melting in the case of a hot-melt adhesive) a particularly good branch-off seal is formed. By far the most widely used technique for causing heat-recovery of the sleeve is a torch, and this can usefully also be used to activate the adhesive in the crutch region: heat can flow by conduction from the outer legs of the clip (which are exposed to the torch) to the adhesive at the inner leg, particularly if the inner leg includes a heat conductor in thermal contact with the outer legs.
Offenlegungsschrift No. 3105471 relates to the same technique of forming a branch-off between cables using a clip. In one embodiment, the clip is essentially u-shaped and has injection moulded to the bridge portion a hot-melt adhesive which is intended to provide a seal in the crutch region. No means is provided for activating this inner leg of adhesive and a good seal is likely to be difficult to achieve. This is because heat conducted from the outer legs will cause adhesive at the bridge portion to melt and flow at least to some extent thus prematurely breaking the heat path to the remainder of the adhesive. The clip is said to be designed to prevent heat damage to the cables at all costs.